1. Field of the Invention
This invention relates to a recording liquid suitable for use in the ink jet system in which recording is performed by permitting liquid droplets to fly through orifices of a recording head or for use in writing tools.
2. Description of the Prior Art
Various types of ink jet recording methods have been actively investigated, because they generate less noise, require no special fixing for recording on a plain paper and also enable high speed recording. The recording liquid to be used in these ink jet recording methods is required to have various characteristics, including property values such as viscosity and surface tension within appropriate ranges, no clogging of a minute discharging outlet (orifice), capability of giving recorded images of clear tone and sufficiently high density, and stability of physical properties or no solid precipitation during storage. In addition to these characteristics, it is also required to have other properties such that recording should be possible without limitation of the materials to be recorded on (hereinafter referred to as recording materials) as represented by paper, that the fixing speed on recording materials should be great, that it should be excellent in water resistance, solvent resistance (particularly alcohol resistance), light resistance and abrasion resistance and also that it can give images excellent in resolution.
The recording liquid to be used for the ink jet recording method is basically composed of a dye as the recording agent and a solvent, and hence the characteristics of the recording liquid are greatly governed by the inherent properties of the dye. Accordingly, it is a very important technique in such a field of the art to select a dye so that the recording liquid may have the characteristics as mentioned above.
In particular, solubility of the recording agent in a liquid medium is important. Namely a sufficient solubility in water as well as in a wetting agent generally composed of an organic solvent is essential for maintaining good anti-clogging property and good solving stability of the recording agent.
On the other hand, in recording a full color image according to the ink jet recording method, three recording liquids of the primary colors of magenta, yellow and cyan, respectively, or four recording liquids of the three primary colors plus black are used, and the tone of the recorded image is given by subtractive mixing of those colors. In this case, in order to obtain a desired tone of the image recorded, the recording liquids are required to have hues exhibiting ideal magenta, yellow or cyan primary color, respectively, and also high chromas. Thus, it is a very important technique to select a dye in consideration of the tone given by the recording liquid.
However, among the recording liquids of cyan color known in the art, particularly the ones containing phthalocyanine type dyes as the recording agent, there were few recording liquids satisfying sufficiently the requirement for the characteristics as mentioned above, particularly the solubility and the tone, and the development of a recording liquid having these characteristics has long been desired.
For example, in the case of a recording liquid containing copper phthalocycnine tetrasolfonic acid or its alkali metal or organic amine salt as the recording agents disclosed in Japanese Laid-open Patent Publication No. 5772/1982, this dye, having 4 sulfonate substituents, is highly soluble in water. However, the following problem has been pointed out: when the recording liquid is left unused in a recording device for a long term, the composition of the recording liquid at the nozzle portion changes due to the evaporation of water which is a more volatile component of the recording liquid, and this change tends to clog the nozzle portion because of the low solubility of the dye in polyhydric alcohols conventionally added thereto as a wetting agent.